Effluent discharge bitumen recovery by settling



Mamh 1970 R. A. BAILLIE 3,502,565

EFFLUENT DISCHARGE BITUMEN RECOVERY BY SETTLING Filed se t s, 1966 LOTATION SCAVENGER ZONE PULP

BOX

' MULLER WATER INVENTOR. ROBERT A. BAILLIE ATTORNEY United States Patent 3,502,565 EFFLUENT DISCHARGE BITUMEN RECOVERY BY SETTLING Robert A. Baillie, West Chester, Pa., assignor to Great Canadian Oil Sands Limited, Toronto, Canada, a corporation of Canada Filed Sept. 9, 1966, Ser. No. 578,303 The portion of the term of the patent subsequent to July 16, 1985, has been disclaimed Int. Cl. Cl0g 1/00 US. Cl. 208-11 6 Claims ABSTRACT OF THE DISCLOSURE The specification discloses a process for recovering bitumen from the effluent discharge from a hot water process for treating bituminous tar sands. The eflluent discharge comprises water, sand, silt and bitumen. The effluent is discharged into a quiescent bitumen flotation zone, is settled to form a bitumen layer on top of the water and the bitumen layer is then separately recovered.

This invention is concerned with an improvement in the hot water process for treating bituminous sands such as Athabasca tar sands and the like. The invention is especially concerned with a method for the recovery of bitumen from the efiluent discharged from the hot water process.

Tar sands which are also known as oil sands and bituminous sands are siliceous materials which are impregnated with a heavy petroleum. The largest and most important deposits ofthe sands are the Athabasca sands, found in northern Alberta, Canada. These sands underlay more than 13,000 square miles at a depth of 0 to 2000 feet. Total recoverable reserves after extraction and processing are estimated at more than 300 billion barrels just equal to the world-wide reserves of conventional oil, sixty percent of which is in the Middle East. By way of contrast, the American Petroleum Institute estimated total United States oil reserves at the end of 1965 at 39.4 billion barrels.

The tar sands are primarily silica, having closely associated therewith an oil film which varies from about 5 percent to 21 percent by weight, with a typical content of 13 weight percent of the sand. The oil is quite viscous- 6 to 8 API gravity-and contains typically 4.5 percent sulfur and 38 percent aromatics.

The sands contain, in addition to the oil and sand components, clay and silt in quantities of from 1 to 50 weight percent, more usually 10 to 30 percent. The sands also contain a small amount of water, in quantities of 1 to 10 percent by weight, in the form of a film around the sand grains.

Several basic extraction methods have been known for many years for the separation of oil from the sands. In the so called cold water method, the separation is accomplished by mixing the sands with a solvent capable of dissolving the bitumen constituent. The mixture is then introduced into a large volume of water, water with a surface agent added, or a solution of a neutral salt in water, which salt is capable of acting as an electrolyte. The combined mass is then subjected to a pressure or gravity separation.

In the hot water method, the bituminous sands are jetted with steamand mulled with a minor amount of hot water at temperatures of 170 to 190 F., and the resulting pulp is then dropped into a turbulent stream of circulating hot water and carried to a separation cell maintained at a temperature of about 185 F. In the separation cell, sand settles to the bottom as tailings and oil rises to the top in the form of a froth. An aqueous mid- 3,502,565 Patented Mar. 24, 1970 dlings layer comprising clay and silt and some oil is formed between these layers. This basic process may be combined with a scavenger step for further treatment of the middlings layer obtained from the primary separation step to recover additional amounts of oil therefrom.

The middlings layer either as it is recovered from the primary process or as it is recovered after the scavenger step comprises water, clay and oil. The oil content is, of course, higher in middlings which have not undergone secondary scavenger steps.

Hereinafter in this specification, the term effluent discharge will be used to described the combined mixture of: (1) middlings material of depleted oil content which has undergone final treatment in the hot water process and which comprises clay, silt, sand and some oil dispersed in water; (2) the sand tailings layer; and (3) other discharged water containing fractions which are not the primary products of the hot water process. The effluent discharge is removed from the process plant as a slurry of about 35 to 55, typically 45, percent solids by weight. Included in the slurry is sand, silt, clay and small quantities of bitumen ranging from about 0.5 to 2.0 weight percent of the total discharge.

Because this efiluent contains oil emulsions, finely dispersed clay with poor settling characteristics and other contaminants, water pollution considerations prohibit discarding the efiluent into rivers, lakes or other natural bodies of water. Numerous suggestions have been made for the management of these large quantities of effluent. One proposal has been to store the efiluent in large evaporation ponds where sand can settle out and some water can evaporate. The water, with or without further treatment, may be then recycled back into the process as part of the feed water.

Another proposal has been to remove sand from the eflluent by a novel percolation step with subsequent storing of water in ponds or settling areas at the foot of the percolation medium. This method is disclosed in United States Patent 3,392,833.

Other suggestions have included settling tanks, storage bins, etc. In each of the proposals which have involved the use of a settling area whether it has been a pond, tank or the like, it has been observed that a portion, in the range of about 25 to 50 weight percent, of the bitumen in the efiluent discharge will float as an oil scum on the settling or storage area even though the bitumen is associated with closely held mineral. It has been surprisingly found that this scum can be separately recovered from the water in the eflluent and treated with the froth product of the hot water process or coked directly to give a satisfactory crude.

It is quite unexpected that the bitumen will float on the water in the settling area since the specific gravity of the bitumen and closely held mineral is greater than that of the water. For example, in a typical settling pond, the bitumen specific gravity measures between 1.05 and 1.10 while the pond water specific gravity measures 1.00 to 1.03. It is thought that the floating phenomenon occurs because of air attached to the bitumen. For example, in the process described in Patent 3,392,833, involving treatment of eflluent in sand pile zones, it appears that the bitumen-mineral becomes associated with some air during the turbulence caused by the distribution of eflluent to the sand zone.

This bitumen scum ranges in depth from about 0.001 to about 1.00 inch and is typically about 0.5 inch in thickness. The quantity of bitumen represented by this scum can be rather significant when large settling or storage areas are involved. For example, in one area 6,400 square feet in size, the bitumen depth was found to be 0.53 inch and the total amount of scum bitumen was estimated at about 7,270 pounds.

Thepresent invention relates to a process for treating Lhe effluent discharge from the hot water process to re- :over this scum forming bitumen. The steps of the process generally comprise discharging the effluent into a quiescent iettling zone, settling the efiiuent in a bitumen flotation :one to form a bitumen layer on top of the water in the effluent and then removing the bitumen layer from the .op of the water for recycle to the hot water process or ;ome other treating step. t

The settling step may be conducted by any method well (nown in the art. About 25 percent of the bitumen con- ;ained in the eflluent floats to the top of the water almost immediately. After about two weeks the bitumen scum :onsists of about 50 percent of the total bitumen contained .n the efiiuent.

The scum may be skimmed by froth wiper devices to a pump and pumped back into the process or collected by any usual method so long as it is collected separately from the pond water. The recovered bitumen may be recycled back into the process to be added into the separation cell, the pulp box, or preferably added to the froth from the separation cell for further treatment.

The drawing is a schematic representation of the bitumen fiow in a typical hot water process for treating Athabasca tar sands.

Oil sand is fed into the system through line 1 where it first passes to a conditioning drum or muller 12. Water and steam are introduced and mixed with the sands. Mulling of the tar sands produces a pulp which then passes from the conditioning drum as indicated by line 2 to a pulp box 13 which serves as a zone for diluting the pulp with additional water before passage to primary separation zone 14.

The separation zone 14 typically comprises a large cylindrical or rectangular tank, or battery of tanks, which may. if desired, be provided with heating coils for maintaining processing temperature. The separator is supplied with an oil froth withdrawal line 4 adjacent to the top and a sand tailings removal line 5 at the bottom. The sep arator also has a withdrawal line 6 through which a stream of middlings layer is removed.

The pulped tar sands are continuously flushed from the pulp box through line 3 into the separator 14 The settling zone in separator 14 is relatively quiescent so that oil froth rises to the top and is withdrawn via line 4 while the sand settles to the bottom as a tailings layer which is withdrawn through line 5.

A middlings layer which contains some oil that failed to separate is withdrawn from the cell through line 6 to a flotation scavenger zone 15. In this zone an air flotation operation is conducted to cause the formation of additional oil froth which passes from scavenger zone 15 through line 7 and thence to line 4 for further processing in admixture with the froth from the primary zone. An oil-lean water middlings stream is removed from the bottom of scavenger zone 15 via iine 8 and is mixed at 16 with tailings from line 5 to form the eflluent discharge.

The'efiiuent discharge is fed through line 9 to a quiescent bitumen flotation zone 17 which may be pond areas, settling tanks, etc. The bitumen layer which forms on top of the water in the settling zone 17 is withdrawn and fed via line 10 to be mixed with the froth or may be withdrawn via line 11 and fed to the pulp box 13 and mixed with feed tar sands or withdrawn and added during any other step inthe hot water process.

The ollo g example il ust ates the inve tion:

4 EXAMPLE An effluent of composition as given in the table is collected from the oil-lean middlings and sand tailings from the hot water process and is percolated through a 300 acre sand slope as described in United States Patent 3,392,833, down to a 200 acre flat pond area enclosed by the slope and by constructed dikes. About 152,500 tons of efiiuent per day is treated in this way.

The efiiuent is continually added at about this average rate. Two weeks after initial addition about 8,400 tons of bitumen has accumulated in the form of a scum on the surface of the water in the pond. At this time removal of the scum is initiated by skimming the bitumen with wiper blades into a pump. The skimmed bitumen is then pumped to the froth processing area where it is added as a diluent to the froth.

The total bitumen scum on the surface of the pond and the amount recycled is calculated and it is determined that 600 tons per day of scum forming recoverable bitumen is distributed into the pond.

What is claimed is:

1. A process for recovering bitumen from the effluent discharge from a hot water process for treating bituminous sands to recover the bitumen therefrom as a froth product, said effiuent discharge comprising water, sand, silt and bitumen, the steps of which comprise:

(a) discharging said effiuent into a quiescent bitumen flotation zone;

(b) settling the said effluent in said bitumen flotation zone to form a bitumen layer on the top of the water of said efliuent; and

(c) separately removing said bitumen layer from said Water.

2. A process according to claim 1 which comprises recycling the bitumen removed from said water to the said hot water process.

3. A process according to claim 1 which comprises adding the bitumen removed from said Water to the froth product of the hot water process.

4. A process of recovering bitumen from the efii-uent discharge from a hot water process for treating bituminous sands to recover the bitumen therefrom as a froth product, said effluent discharge comprising sand, silt and bitumen, which comprises:

(a) percolating the efliuent down an inclined sand pile zone to remove the sand from said eflluent; and

(b) discharging said percolated efliuent into a quiescent bitumen flotation zone;

(0) settling the said eifiuent in said bitumen flotation zone to form a bitumen layer on the top of the water of said efiiuent; and

(d) separately removing said bitumen layer from said Water.

5. A process according to claim 4 which comprises recycling the bitumen removed from said water to the said hot water process.

6. A process according to claim 4 which comprises adding the bitumen removed from said water to the froth product of the hot water process.

References Cited UNITED STATES PATENTS 2,980,600 4/1961 Keliey 2081l 3,392,833 7/1968 Baillie 21065 DELBERT E. GANTZ, Primary Examiner T. H. YOUNG, Assistant Examiner 

